How do cars measure fuel level accurately when the fluid is constantly sloshing around?
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Even if there is sloshing as long as the average is correct you can filter the output. You can add analog or digital filters that limit the rate the level can change so what is shown is an average of recent measurements. It would be possible with a mechanical system too.
I would disagree taht the measurement is accurate, if you introduce a constant error from going up or down a hill, part at an incline or even accelerating or breaking there is some change. It is most of the time hard to spot because the gauge in the car does not have a fine graduation, the time you notice the problem is if just reach the low fuel light level then it will turn on and off when you drive. In a modern car where everything is computer controlled, you can hide that blinking by adding some hysteresis like turning on the light when the level reaches 10% and keeping it on until it reaches 15%.
I am also skeptical if the fault is linear or not. Tanks are often not completely symmetrical so before there was a computer in between I suspect there was not the same amount of fuel change for the same amount of gauge movement along the whole range. I suspect that is why gauges often just have quarter tank steps.
Cars do not use the fuel gauge to calculate fuel usage, they use the pumped volume which is a lot more accurate.
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